This invention relates generally to the field of control systems for controlling the position of a suspended boom and, more specifically, to a control system for automatically controlling the roll of a boom.
Suspended booms are used in many different industries for different purposes. In the agricultural industry, for example, a suspended boom sprayer is commonly used for the application of pesticides, herbicides and fertilizers. Spray tips are mounted to the sprayer boom at a predetermined spacing to promote an even application of the material being applied. In order to achieve a reasonably uniform application of such material it is necessary that the spray tips be maintained at a constant (or near constant) distance from the ground or vegetation to which the material is being applied. Generally, the spray tips used for these applications are designed for use at a specific height for optimum performance and application uniformity.
Maintaining a uniform height at all points of a boom is a difficult challenge. The boom of a boom sprayer is suspended mechanically from the frame of the sprayer and, as the sprayer moves over uneven ground, different adjustments of position are required to maintain a uniform boom height over the whole length of the boom. Any of three independent position adjustment mechanisms are typically used for this. First, a vertical height adjustment mechanism is known for lifting (or lowering) the entire boom assembly in a vertical direction. Second, left and right wing tip adjustment mechanisms are known for independently lifting (or lowering) either wing section of the boom. Third, a roll adjustment mechanism is known for rotating the entire boom in a clockwise, or counterclockwise, direction about an axis pointing in the forward direction (this being useful to keep the entire boom parallel to the ground when a height error is introduced by the supporting vehicle as its wheels drive over uneven ground). To date, the known roll adjustment mechanisms have used either passive means for controlling the roll (e.g. in the form of a rotation or pendulum coupling between the sprayer frame and the center boom, together with a damper for dampening the rotational action and centering the boom so that the boom will eventually approach a parallel condition with the sprayer main frame) or a manually operated hydraulic cylinder (e.g. directly or indirectly with the use of springs and dampers). Prior attempts to automate the roll position of the boom have been largely unsuccessful and there is a need in the industry for an effective, automated roll control system.
Controlling the boom roll provides a number of advantages which serve to improve the performance of a boom operator and faster operation. Specifically, roll control can remove errors induced by the vehicle, when the vehicle moves over uneven ground and, at the same time, it may also serve to adjust the tips by increasing the rate of adjustment of the tip heights when a roll error exists. Automatically controlling boom roll can also help to more quickly stabilize the roll action of the boom (i.e. the back and forth swinging of the boom caused by the pendulum action of a roll), as compared to passive control means relying only on the friction and mechanical dampers to reduce this swinging, thereby producing a more stable boom, with a more consistent height, in all field conditions.
There is a need for improved automated boom roll control means. There is also a need for means by which a combination of boom position parameters may be considered for purposes of controlling the boom roll. Further, there is a need for means by which real time operating parameters are used to control the boom roll.
In accordance with the invention there is provided a roll control system for controlling a roll position of a boom coupled to a support frame to permit clockwise or counterclockwise rotation relative thereto, the boom comprising left and right wing sections and the roll position representing a measure of such rotation. A roll control mechanism is configured for rotating the boom relative to the support frame in response to a roll control signal provided thereto. Wing section position measuring apparatus is configured for producing a right wing signal correlatable to a distance between the right wing section and a right wing reference position (e.g. ground) and a left wing signal correlatable to a distance between the left wing section and a left wing reference position (e.g. ground). Boom roll position measuring apparatus is configured for producing a boom roll signal correlatable to a roll position of the boom. A controller (e.g. a microprocessor) is configured for identifying a wing section differential value and a boom roll value derived from the right and left wing signals and the boom roll signal, respectively, and for identifying a boom roll control error value derived from the wing section differential value and the boom roll value, the boom roll control error value being configured for deriving therefrom the roll control signal. Preferably, the wing section differential value is scaled by a first scaling factor and the boom roll value is scaled by a second scaling factor.
The wing section position measuring apparatus may comprise a first distance measuring component configured for producing the right wing signal and a second distance measuring component configured for producing the left wing signal. The boom roll position measuring apparatus may comprise a third distance measuring component configured for producing the boom roll signal. The first, second and third measuring components may comprise ultrasonic sound echo sensors. The first measuring component is preferably located at or near a terminal end of the left wing section and the second measuring component is preferably located at or near a terminal end of the right wing section.
In one embodiment, the roll control mechanism comprises a roll frame coupled to the support frame by a pivotal coupling and by extension/retraction means (e.g. a hydraulic valve and cylinder) spaced from the pivotal coupling. In this embodiment the third measuring component is located on the roll frame and preferably at least one spring and a damper couple the roll frame and the boom.
Preferably, the controller compares the boom roll control error value to a deadband value and sets the boom roll control error value to zero when the comparison identifies that the boom roll control error value is less than the deadband value.
In accordance with a further aspect of the invention there is provided a method for controlling the roll position of a boom comprising, producing a right wing signal correlatable to a distance between the right wing section and a right wing reference position; producing a left wing signal correlatable to a distance between the left wing section and a left wing reference position; producing a boom roll signal correlatable to a roll position of the boom; deriving a wing section differential value and a boom roll value from the right and left wing signals and the boom roll signal, respectively; deriving a boom roll error control value from the wing section differential value and the boom roll value; producing a roll control signal using the boom roll error control value; and, rotating the boom relative to the support frame in response to the roll control signal. Preferably, the wing section differential value is scaled by a first scaling factor and the boom roll value is scaled by a second scaling factor. Preferably, the boom roll control error value is compared to a deadband value and the boom roll control error value is set to zero when the comparison identifies that the boom roll control error value is less than the deadband value.